WordPress at a glance
filter is not described

preprocess_comment filter-hook . WP 1.5.0

Filters a comment's data before it is sanitized and inserted into the database.

Usage

add_filter( 'preprocess_comment', 'filter_function_name_3109' );
function filter_function_name_3109( $commentdata ){
	// filter...

	return $commentdata;
}
$commentdata(array)
Comment data.

Where the hook is called

wp_new_comment()
preprocess_comment
wp-includes/comment.php 1946
$commentdata = apply_filters( 'preprocess_comment', $commentdata );

Where the hook is used (in WP core)

Does not used.